The invention relates to a gas-generating device or inflator suitable for rapidly inflating a flexible bag or filling a container to an elevated pressure. More specifically, this invention relates to a gas-generating device capable of modulated pressurization.
Rapid gas-generating devices or inflators, as they are referred to in the art, have found widespread use. One use is in passive air bag restraint systems in order to reduce the large number of deaths and injuries occurring in automobile accidents annually. Air bags and inflatable belts for passive restraint systems are operatively associated with inflator devices which are generally activated by an inertial switch or sensor which detects rapid deceleration of a vehicle such as that which occurs upon impact between an automobile and another object. When the inertial switch is triggered, it causes an inflator to inflate a collapsed flexible bag or belt quickly which is deployed into a protective position in front of the occupant. The bag or belt must inflate extremely rapidly after the primary impact or collision in order to protect the occupants from injury caused by secondary impact or collision with the interior of the vehicle. In order to meet such criteria, the bag or belt should be fully inflated within about 10-65 milliseconds after inflation has been initiated.
A variety of conflicting considerations must be taken into account in developing an effective air bag passive restraint system. First, the inflator must be capable of producing and/or releasing a sufficient quantity of gas to the air bag within the time limitation required of a passive restraint air bag system, given the time limitation involved in air bag restraint systems, roughly about 10 to 15 milliseconds for side impact applications and about 30 to 65 milliseconds for driver and front passenger applications. Inflators must be capable of filling an air bag in these time frames with 15 to 50 liters of gas for side applications and 60 to 200 liters of gas for driver and front passenger applications. The specific amount and rate of gas generation or release is determined by the required air bag volume and the vehicle structural rigidity which influences the time between primary and secondary impacts.
Other considerations in designing an inflator for a passive air bag restraint system, particularly for automotive applications, include the toxicity and noxiousness of the gas which fills the air bag. That is, for air bags that deflate by releasing gas into the confines of the interior of the vehicle and in the case where the airbag ruptures, the inflator for an automotive air bag must generate or release gas and other materials which meet or surpass certain non-toxicity requirements in order to protect the occupants. Otherwise, toxic or noxious gas may injure or cause illness to the occupants. For example, the release of too much carbon monoxide could cause illness and even be deadly to the occupants. These toxicity requirements are controlled by certain specifications required by the automotive manufacturers. For example, a typical automotive requirement is that an inflatable air bag system meet certain specifications for a 100 cubic foot compartment. These toxicity specifications are set by health requirements and one reference which is helpful in defining those requirements is OSHA workplace breathing air standards, another reference is the American Conference of Governmental Hygienists"" Allowable Limits for Short Term Exposure Levels for the Workplace.
In addition, the gas-generating composition may be highly toxic or unstable requiring special handling during the manufacturing process and creating disposal problems at the end of the useful life of the vehicle. For example, raw sodium azide which is used as the gas-generating composition in most airbag inflators today has a relatively high toxicity which creates handling problems during the manufacturing process.
Other considerations include that the gas and any other materials, for example solid particles, released into the air bag must meet energy transfer restrictions so that it will not burn or deteriorate the integrity of the air bag. Insuring that the energy and materials transferred during the inflation event do not burn, puncture or deteriorate the bag, protects the occupants from injury and insures proper bag inflation.
Packaging restrictions add a further consideration in the development of passive air bag inflators. For example, weight and size are primary factors in determining the suitability of vehicle inflator embodiments. Weight reduction translates into fuel economy improvements and size reduction into styling and design flexibility. For styling reasons and customer-acceptance, and so as not to interfere with the occupants"" movement, comfort or the driver""s line of vision, it is desirable to arrange the inflator so as not to be obtrusive, and yet have it positioned so that it effectively accomplishes its intended task. In order to accomplish these styling, customer-acceptance and engineering design parameters, the inflator must be capable of being packaged in a compact manner. For example, it is desirable to package the inflator in an air bag module which fits with the hub of the steering wheel while still allowing the use of the vehicle""s horn by depressing any part of the steering wheel hub and while additionally allowing the use of the numerous control switches and stalks on the steering column. It is further advantageous for side impact bags to package the inflator and air bag module between the exterior door panel and the trim or panel in the interior of the door.
The emphasis on weight reduction for the purpose of fuel conservation in motorized vehicles, and the recent development of passenger air bags, rear-seat occupant air bags, side-impact air bags, seat-belt air bags and knee-bolster air bags as well as the contemplated use and development of air bags in the A and B pillars of vehicles and other small bags of 1 to 30 liters of volume, have created the need and demand for a light and compact inflation system.
There are basically two methods or systems which are employed to supply the gas in air bag restraint systems. In one method, the inflating gas is provided as a compressed gas stored onboard the vehicle within a pressure vessel. In the second method, the bag is inflated by igniting a pyrotechnic gas-generating propellant composition and directing the resultant gaseous combustion products into the bag. These two methods create three categories of inflators, the first relies solely upon a pressurized reservoir of gas, the second upon burning a combustible propellant to generate all of the gas to fill the air bag, the third upon a combination of the two described methods to inflate the air bag, and is known in the art as a hybrid inflator.
The first method requires a reservoir of gas stored onboard the vehicle at a very high pressure which is discharged into the bag immediately upon sensing the impact. In order to inflate the vehicle occupant restraint bag in the required time of 0.010 to 0.065 seconds, that is to attain a fill volume rate of at least about 900 liters per second and preferably approximately 3,000 liters per second, a relatively large reservoir of gas at pressures of 3,000 pounds per square inch (xe2x80x9cpsixe2x80x9d) is stored in a pressure vessel. To open the pressure vessel in the short time interval required to inflate the air bag, explosive actuated arrangements are employed for bursting a diaphragm or cutting through a structural portion of the reservoir.
In the second method, a pyrotechnic gas generator having an ignitable and rapid-burning gas-generating propellant composition burns to produce substantial volumes of hot gaseous products which are directed into the inflatable bag. These gas generators must withstand thermal and mechanical stresses during the gas-generating process. Specifically, the gas-generating propellant ignites, combusts and burns at elevated temperatures and pressures which require the casing (pressure vessel) surrounding the gas-generant to be capable of safely withstanding these elevated pressures at a specified safety factor. These strength requirements result in a large, bulky and heavy inflator typically of toroidal shape for driver-side applications.
Typically, there is a center chamber in these gas-generating inflators used for pyrotechnic ignition-enhancers and auto-ignition materials (xe2x80x9cAIMxe2x80x9d). The center chamber is concentrically surrounded by one or more separate chambers in fluid connection with each other and with the center chamber, the concentric chamber typically contains the main propellant charge and filter. Structural members divide the concentric chambers and are connected to the outer pressure vessel usually by means of a weld, rivet, screw thread or other mechanical fastening means. These structural members typically form a central post construction for the pressure vessel which adds to the strength, weight and size of the inflator.
Pyrotechnic compositions typically comprise a fuel and an oxidizer. Because gas-generants, including sodium azide which is used today in most passive restraint systems, and most pyrotechnic oxidizers typically produce significant amounts of solid particulates, filters are typically incorporated into the inflator to separate the hot particles from the gas prior to exhausting the inflating gas into the air bag. The solids produced during combustion are separated from the gas stream to prevent the particles from rupturing the bag and injuring occupants. In addition, as described above, it is important to produce an inflator gas having a temperature which is sufficiently low to avoid burning or deteriorating the integrity of the air bag or belt. However, gas-generants which burn faster and better at lower temperatures tend to produce significant quantities of particulates making filters all the more important when using these low temperature-burning gas-generating materials.
In addition, the filters in prior art inflators also acted as a heat sink to reduce the temperature of the gaseous products filling the air bag. The filters which are usually made from metal are helpful in absorbing the heat from the gaseous products and often provide a torturous path for the gaseous products to travel which further absorbs the energy of the gaseous products in order to protect the integrity of the air bag or belt.
The structural members forming the central post construction and filters in these gas-generating inflators add weight, complexity, cost and bulk to the inflators. For the reasons described, decreasing weight and size are desirable in the design of automotive inflators for passive air bag restraint systems. Although there have been inflator designs which have deviated from these typical designs, they still include the disadvantages of filters or central post construction or other bulky designs. For example, U.S. Pat. No. 5,556,130 describes a pyrotechnic inflator having a generally cylindrical pressure vessel formed of sheet metal which includes an annular filter comprising a plurality of convolutions of metal screen having decreasing mesh size as it progresses to the outside of the filter where it abuts against the pressure vessel walls. U.S. Pat. No. 4,923,212 discloses a pyrotechnic inflator having a domed pressure vessel which includes an annular filter abutting against the pressure vessel walls. In both of these patents, the filter adds to the weight, size and complexity of the inflator design.
U.S. Pat. No. 5,551,725 discloses several inflator embodiments. Two embodiments include a cylindrical tubularly-shaped pressure vessel which is relatively bulky, having a length substantially larger than its diameter and which relies on the ignition-enhancing materials being blown into the portion of the pressure vessel containing the gas-generant composition to provide quick and efficient mixing and burning with the main gas-generant. This embodiment disadvantageously relies on a bulky, large and inconveniently shaped pressure vessel which is difficult to use in many applications and is not sized to be a drop-in replacement for existing inflators. The other embodiment of the invention disclosed in U.S. Pat. No. 5,551,725 relies on a toroidally-shaped pressure vessel having a structural central post structure which disadvantageously adds to the bulk, weight and complexity of the inflator.
The third category, the hybrid inflation system, utilizes a gas-generating propellant composition and a pressurized medium to meet the requirements of air bag restraint systems. As such, a hybrid inflator suffers many of the drawbacks of the other two categories of inflator designs, and is often of complex configuration. These hybrid systems typically store pressurized gas at about 3,000 psi. In operation, they burn gas-generating propellant grains to produce heated gas as well as to heat the stored gas. Hybrid inflators produce less solid particles since less solid particulate producing gas-generant can be used to obtain the same inflator gas output. In addition, the stored pressurized gas cools the gas which flows into the inflator.
The combination of greater condensation of solids within the inflator and the reduction of solids produced allows some hybrid inflators to operate without filters. Current driver-side hybrid inflators are toroidal in shape with a center chamber typically used for the hybrid heater assemblies surrounded by one or more separate chambers in fluid connection typically containing the pressurized gas. Structural members divide the concentric chambers and are connected to the outer pressure wall usually by weld, rivet, screw thread or other mechanical fastening means. Hybrid inflators have a number of drawbacks: first they are more complicated and have more parts. Second, there is higher cost associated with more parts and the additional handling and assembly operations. Third, they are larger and heavier because the inflator energy is in part stored as a pressurized gas rather than a solid and fourth, they have decreased reliability resulting from storing the pressurized gas over the lifetime of the vehicle.
Recent efforts aimed at making passive occupant restraint systems even more effective at reducing the risk of injuries have called for the development of advanced air bags. Such air bags should be able to modulate or otherwise control air bag deployment based upon the size, weight and/or location of the vehicle occupants. Previous attempts to compensate for the size differential between, for instance, a child and an adult include U.S. Pat. No. 5,310,214 directed to an air bag system having an air bag made of two separate gas sources in an attempt to protect both a child and an adult and U.S. Pat. No. 5,058,921 directed to an inflator module arranged to simultaneously develop, within a single air bag, two different inflation zones. However, these attempts have not taken into account the location of the occupants relative to the airbag nor have they modulated the deployment of a single airbag by providing bag inflation modulated between two different gas output levels.
Additional efforts have been directed to producing a gas discharge equivalent to having two discrete inflators capable of being fired independently. Such dual discharge inflators typically have a first discharge which is 60-70% of the discharge level provided by an inflator sized to protect an unbelted 50th percentile (or average size) male adult. This first discharge provides a lower gas inflation rate to the airbag as well as a lower total amount of gas with which to fill the bag at the completion of the inflation event. The reduced inflation rate results in lower bag velocities while the airbag is exiting the airbag module.
The second discharge is provided by these dual discharge inflators when both discrete inflators are fired simultaneously. The second discharge, equal to the sum of the discharges of two independent inflators, is generally sized to provide an output adequate to protect an unbelted 50th percentile adult male. The second discharge provides both the maximum gas inflation rate and maximum total amount of gas with which to fill the bag.
It is thus an object of the present invention to provide an inflator with reduced weight, size and with fewer geometric constraints on its design and packaging. It is a further object to provide a simple, compact and light-weight inflator. It is a still further object to eliminate the need for a filter in an inflator. It is another object to provide a gas-generating inflator which eliminates or at least reduces the size of internal structural members of the pressure vessel and their attachment means. It is a further object of the invention to provide a less costly inflator both in terms of fewer parts and fewer and less costly manufacturing operations to assemble and which yet may serve as a drop-in replacement for existing toroidal driver-side air bag inflators. Another object of the invention is to provide a dual stage driver inflator having a single pressure vessel that is capable of producing a modulated output with respect to the speed and force of an air bag deployment between a first minimum level and a second maximum level based upon sensor input relating to such factors as crash severity, seat-rack position, occupant weight and/or size, occupant location relative to the air bag, and whether or not the occupants are wearing seat belts.
These objects are achieved by the use of a non-azide, filterless, gas-generating, pyrotechnic, inflator which eliminates the structural members which typically divide the concentric chambers and which are connected to the outer pressure vessel walls in a toroidally-shaped inflator. The present invention comprises a non-hybrid pyrotechnic filterless inflator, i.e., gas generator, configured and adapted to provide a sufficient amount of non-toxic, non-noxious gaseous product by the combustion of a non-azide pyrotechnic propellant composition stored within a housing (pressure vessel) for substantially inflating an automotive passive restraint air bag device in the time period between the occurrence of a primary collision between the vehicle and another object and a secondary collision occurring between the occupant(s) and the interior of the vehicle.
The inflator of the present invention comprises a generally discoidally-shaped pressure vessel formed of a cup-shaped base member defining a central opening which receives an initiator assembly and a cup-shaped closure cap defining at least one exhaust nozzle for directing gaseous products out of the inflator and into the air bag. As used herein the term xe2x80x9cdiscoidalxe2x80x9d or xe2x80x9cdiscoidally-shapedxe2x80x9d when used with reference to a pressure vessel refers to a pressure vessel having a shape wherein the diameter is greater than or about equal to its height and which lacks the central post structure forming a separate central chamber that is typical of prior art toroidal pressure vessel structures. An environmental seal may be provided over the exhaust nozzle to prevent contamination of the interior components of the inflator during periods of non-use and to allow pressure to build up within the inflator upon initiation of the pyrotechnic reaction. The pressure vessel may advantageously contain a mechanical interface for connecting the inflator to the air bag module.
A gas-generant assembly comprising a stamped metal cup which contains the main pyrotechnic gas-generating propellant composition is positioned about and in some embodiments in contact with the initiator assembly and preferably spaced a small distance from the walls of the pressure vessel. The gas-generating composition is preferably a low solids producing formulation configured in the form of pellets or tablets. The gas-generant cup contains numerous openings along its walls for allowing the gaseous products produced by the combustion of the gas-generating propellant composition to escape the gas-generant cup. These openings are preferably configured to be smaller than the size and configuration of the gas-generating composition pellets. Preferably, the gas-generating cup assembly includes a spring-loaded lid to keep the gas-generating pellets from moving within the inflator which can cause disturbing rattling noises and also deterioration and crumbling of the gas propellant tablets and resulting leakage of the gas-generating composition outside of the gas-generant assembly. The gas-generating cup is not attached to the closure cap and forms no structural part of the pressure vessel but acts as a receptacle to position the gas-generating composition about the initiator assembly. The initiator assembly comprises an initiator plug received in the central opening in the base member, a standard initiator which ignites the gas-generating products or ignition-enhancing materials in the inflator and electrical connections to connect the initiator to a crash-sensing diagnostic system.
In an alternate embodiment, the inflator also may contain an enhancer cup assembly which comprises a stamped metal cup defining numerous gas ports about its walls and an ignition-enhancing charge material placed inside the cup. The gas ports in the cup are sealed with a burst foil to prevent migration of the ignition-enhancing charge and to allow a build up of pressure within the enhancer cup before burst of the foil seal. The enhancer cup is positioned about the initiator assembly to place the ignition-enhancing charge about and in contact with the initiator. The ignition-enhancing material provides sufficient heat and pressure to ignite the main gas-generating composition and is preferably a fast-burning, low solids-producing formulation. The enhancer cup is not attached to the closure cap and forms no structural part of the pressure vessel of the inflator. In this embodiment, the gas-generating cup assembly is positioned concentrically about the enhancer cup assembly.
In another embodiment, the inflator also may contain an AIM (xe2x80x9cauto-ignition materialsxe2x80x9d) assembly to provide safe ignition of the main gas-generating composition of the inflator when it is subject to a bonfire environment. The AIM assembly comprises AIM powder packaged in a thin metal cup containing a seal. The AIM assembly can be used in conjunction with or alternatively without the enhancer cup assembly. The AIM cup is preferably in abutting relationship with at least one wall of the pressure vessel.
The advantages of the present inflator design are a smaller package with a simpler, lighter and less costly design. The lower cost of the gas-generating inflator of the invention is achieved through the elimination of or lighter weight internal structural hardware and their attachments. The lower cost is achieved also by eliminating the filter typically found in most gas-generating inflators. The lower cost of the inflator of the invention is achieved also because fewer and less costly manufacturing operations are required to assemble the inflator. The invention is advantageous also because of its smaller, more compact size. The size advantage also is achieved by eliminating the filter and by eliminating or reducing the heft, strength and bulk of any internally fastened structural center post components thereby resulting in a lighter, smaller inflator.
In another embodiment, the present invention is directed to a dual stage inflator capable of producing at least a first output level and a second output level. The dual stage inflator includes a pressure vessel having at least one exhaust nozzle adapted to permit passage of gases within the pressure vessel out of the pressure vessel. The pressure vessel includes a first chamber. The first chamber includes a first gas-generant charge present in an amount sufficient to generate the first output level and a first initiator assembly adjacent said first gas-generant charge and capable of initiating said first charge. The pressure vessel also includes a second chamber. The second chamber includes a second gas-generant charge present in an amount sufficient to generate enough output to combine with the first output level to form the second output level and a second initiator assembly adjacent the second gas-generant charge and capable of initiating said second charge independent of the first charge.
In another embodiment, the second chamber is separated from the first chamber by a one-way seal permitting passage of gas from the second chamber to the first chamber but inhibiting passage of gas from the first chamber to the second chamber.
In yet another embodiment, the first chamber further may include a first gas generant cup having sidewalls and containing the first gas-generant charge and a lid positioned across an open top of the first gas-generant cup. In this embodiment, the second chamber is disposed within the sidewalls. In still yet another embodiment, the second chamber includes a cylinder having a bottom and a top and extending into the first chamber, the cylinder bottom sealed against the pressure vessel and the cylinder top sealed by the one-way gas seal. The first gas-generant cup may also include a plurality of gas ports disposed around the sidewalls. The gas ports are not aligned with the exhaust ports in the pressure vessel.
In order to protect the dual stage inflator from excessive temperatures, the inflator may include an auto-ignition powder for igniting the gas-generating charge at a temperature lower than ignition temperature of the gas-generating charge. In another embodiment, the auto-ignition powder is disposed adjacent the cylinder bottom in the second chamber and is bounded by cylinder walls, an internal collar of the second initiator assembly sealing the cylinder bottom, and a pad. In yet another embodiment, the auto-ignition powder is disposed within a cartridge, and the cartridge passes through the first gas-generant cup into the first chamber.
In order to release gases, the pressure vessel may include two exhaust nozzles disposed on opposite sides of the pressure vessel, and the inflator may include a shroud covering the pressure vessel. The shroud includes a plurality of vents disposed around the shroud, the vents not aligning with the exhaust ports. In another embodiment, the vents are spaced around the shroud at an angle from about 42xc2x0 to about 48xc2x0.
The inflator may further include a sensor connected to the first and second initiator assemblies and capable of initiating the initiator assemblies either independently or simultaneously. In another embodiment, the sensor detects rapid vehicle deceleration and initiates the initiator assemblies based upon vehicle speed, crash severity, seat rack position, passenger weight, passenger size, passenger location, seat belt use, or combinations thereof. The sensor can be provided in the inflator itself or as an independent assembly.
The second initiator assembly can be initiated after the first initiator assembly. Alternatively, the second initiator assembly can be initiated after the first initiator following a delay after the initiation of the first initiator of about greater than 0 milliseconds to about 40 milliseconds.
Examples of the gas-generant charges include a non-azide, low-solids producing gas-generating composition. The composition produces a gaseous product upon combustion. The gas-generating composition includes guanidine nitrate, and an oxidizer comprising a mixture of ammonium perchlorate and sodium nitrate. In another embodiment, the inflator includes from 54 to about 67 percent guanidine nitrate and from about 33 to about 46 percent oxidizer wherein the oxidizer includes ammonium perchlorate and sodium nitrate in a mole ratio of about 1 mole of ammonium perchlorate to about 1 to about 4 moles of sodium nitrate. In yet another embodiment, the gas-generating composition includes about 55-65 percent guanidine nitrate, about 20-25 percent ammonium perchlorate and about 15-20 percent sodium nitrate. In still yet another embodiment, the gas-generating composition includes about 59 percent guanidine nitrate, about 23 percent ammonium perchlorate and about 18 percent sodium nitrate.
The present invention includes an air bag system or use in an automobile. The air bag system includes an air bag having an open end and the dual stage inflator of the present invention disposed in the open end for modulating the inflation rate of the air bag at between either a first or a second rate and the inflation amount between either a first or a second peak upon detection of rapid vehicle deceleration.
The present invention is also directed to a method or producing either a first gas output level or a second gas output level for charging a pressurizable container. This method includes determining a desired output level and producing either a first output level having a first mass flow rate and a first total mass of gas or a second output level having a second mass flow rate and a second total mass of gas, wherein the ratio of the second total mass of gas to the first total mass of gas is less than the ratio of the second mass flow rate to the first mass flow rate. In the case of a pressurizable tank, the mass flow rate corresponds to the change in pressure over time (dp/dt), and the total mass of gas corresponds to the peak pressure in the tank.